1Introduction

KEY MESSAGES

There is increasing recognition that overweight and obesity are not just problems of individuals, but also societywide problems that have serious health consequences and costs and affect some population groups more than others. Acting on this recognition will require multifaceted, population-based changes in the social and environmental1 factors that influence energy intake and expenditure.

There is a pressing need to act on the problem of obesity, but there is also a large gap between the types and amount of evidence deemed ideal as the basis for taking action and the types and amount of information available to meet that need.

The Committee on an Evidence Framework for Obesity Prevention Decision Making was formed to address the issues of how to identify, use, and evaluate evidence to inform obesity prevention decisions and how to generate evidence where it is lacking.

This report focuses on the challenge of obesity prevention, viewed from a population or public health perspective. It is about how to increase the likelihood that the decisions made in the many domains that influence obesity prevention will bring about the desired results. Observations of increases in weight among adults and youth globally within just a few decades have forced a paradigm shift in which overweight and obesity are understood not just as problems of individuals, but also as societal problems, affecting whole populations. Causal explanations and pathways to potential solutions have changed accordingly. The relatively rapid upward trends in average weight levels can in large part be explained by changes in social and environmental

1

The term “environmental” refers in this report to people’s cultural, socioeconomic, and physical contexts.

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1
Introduction
KEY MESSAGES
• There is increasing recognition that overweight and obesity are not just problems of individuals, but
also societywide problems that have serious health consequences and costs and affect some population
groups more than others. Acting on this recognition will require multifaceted, population-based changes
in the social and environmental1 factors that influence energy intake and expenditure.
• There is a pressing need to act on the problem of obesity, but there is also a large gap between the
types and amount of evidence deemed ideal as the basis for taking action and the types and amount of
information available to meet that need.
• The Committee on an Evidence Framework for Obesity Prevention Decision Making was formed to
address the issues of how to identify, use, and evaluate evidence to inform obesity prevention decisions
and how to generate evidence where it is lacking.
T his report focuses on the challenge of obesity prevention, viewed from a popula-
tion or public health perspective. It is about how to increase the likelihood that
the decisions made in the many domains that influence obesity prevention will bring
about the desired results. Observations of increases in weight among adults and youth
globally within just a few decades have forced a paradigm shift in which overweight
and obesity are understood not just as problems of individuals, but also as societal
problems, affecting whole populations. Causal explanations and pathways to poten-
tial solutions have changed accordingly. The relatively rapid upward trends in average
weight levels can in large part be explained by changes in social and environmental
1 The term “environmental” refers in this report to people’s cultural, socioeconomic, and physical contexts.

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variables that influence energy intake and expenditure—and the evidence of these
changes is readily available and consistent.
Changes in the food and physical activity environments have caused sustained
positive energy balance, leading to weight gain. For example, energy-dense foods and
beverages have become more inexpensive, heavily advertised, and readily available
than in the past, and their portion sizes continue to increase. Technological innovation
in the home, workplace, and schools has reduced the need for physical effort, leading
to sedentary behavior. Many schools have reduced or eliminated recess and physical
education programs (IOM, 2005). The field of obesity prevention has made advances
in determining the causes of the epidemic, but the complex interrelationships among
those many causes have been difficult to address adequately within a given interven-
tion. For this reason, a systems approach to obesity prevention is advocated in this
report (see Chapter 4).
Taking a population perspective on obesity does not negate the importance of
genetic or biologically mediated influences on the problem. But the increasing preva-
lence of obesity in diverse populations reveals the limitations of biological controls on
energy balance in the face of high caloric availability and diminished caloric expen-
diture through routine physical activity. Nor does the recognition of environmental
influences on obesity negate the importance of individual weight control efforts; how-
ever, the level of effort required makes individuals’ attempts to control their weight
notoriously ineffective over the long term. Changes in aspects of society that encour-
age excess caloric consumption and sedentary behavior are therefore necessary to
support individual efforts to achieve and maintain energy balance. In fact, measures
that have been recommended for populationwide obesity prevention would enhance
the potential for obesity treatment to be effective over the long term. Moreover,
unless both weight gain trends and average population weight levels decline, progress
achieved through treatment for those who are already obese will be offset by the tide
of new people needing such treatment.
Calls for multifaceted efforts to prevent obesity have been made repeatedly by
governments, scientific and professional societies, advocacy groups, and funding agen-
cies at the local, state, national, and international levels. The case for obesity preven-
tion is especially strong in relation to children and youth. The case was made for U.S.
children in a 2005 Institute of Medicine (IOM) report Preventing Childhood Obesity:
Health in the Balance—a report that was generated in response to a congressional
request for a national action plan addressing the problem. Protecting children from
harm and creating social and environmental conditions that support healthy growth
and development are fundamental responsibilities of all societies. The physical and
psychosocial consequences of obesity begin in childhood and may have a lifelong
impact, especially—although not only—if obesity persists into adulthood. Indeed,
most obesity and obesity-related diseases develop during adulthood—an important
justification for obesity prevention directed at the adult population as well. Another
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critical justification is that an obese adult population is an incubator, biologically and
environmentally, for childhood obesity.
This chapter describes the charge and scope of the IOM Committee on an
Evidence Framework for Obesity Prevention Decision Making, as well as the approach
the committee took to fulfill its task. It also sets forth the case for viewing obesity as
a problem of whole populations and for conceptualizing prevention strategies from a
population perspective. Finally, it provides an orientation to the broad array of deci-
sions of potential interest with respect to obesity prevention.
STUDY CHARGE, APPROACH, AND SCOPE
Several prior IOM committees have faced the need to work around evidence gaps
and the fact that evidence hierarchies applied to medical treatment have limita-
tions for assessing population-based preventive interventions. A committee tasked to
develop a national action plan for child obesity prevention ultimately developed a set
of principles to guide its process for reviewing evidence and making recommenda-
tions. These principles underscored the need for evidence to “inform and guide policy
and programmatic decisions.” That committee also emphasized that the “absence of
experimental evidence does not indicate a lack of causation or the ineffectiveness of an
obesity prevention intervention,” that circumstances warrant taking preventive actions
“even if there is as-yet-incomplete scientific evidence on the interventions,” but also
that “there is an obligation to accumulate appropriate evidence not only to justify a
course of action but to assess whether it has made a difference” (IOM, 2005, pp. 111,
114). The committee defined evidence broadly to include several types of quantitative
and qualitative research studies or data that it consulted as appropriate to the type of
question being answered and used an integrated approach that included multiple types
of evidence, drawing on an approach then under development by an international
organization. One of the hallmarks of the committee’s report was the use of historical
case analyses—a social science method—applied to other complex public health sce-
narios as an alternative to typical traditional biomedical research studies.
The specific need for evidence on the effectiveness of interventions undertaken
in various sectors and contexts was addressed by the IOM Committee to Assess
Progress in Preventing Childhood Obesity (IOM, 2007). The IOM Committee on
Food Marketing to Children and Youth (IOM, 2006) also highlighted several evidence
issues and gaps that influenced its systematic review of evidence linking food and bev-
erage marketing to childhood obesity or its behavioral determinants. Most recently,
the IOM Committee on Local Government Actions to Prevent Childhood Obesity
(IOM, 2009) followed the previous IOM recommendation to use the “best available
evidence” rather than wait for the “best possible evidence” (IOM, 2005, p. 3) to rec-
ommend obesity prevention approaches based on potential effectiveness, impact, and
suitability for local settings and authority. In light of the limitations of the current evi-
dence base, that committee chose not to rank the recommended approaches. This deci-
Introduction

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sion was based on a desire to avoid the risk of prematurely devaluing approaches that
are promising but still evolving and recognition that many context-specific factors,
including the level of community support and the costs involved, determine which
approaches are the best fit for a given community.
These evidence issues are not new and have already been the focus of many
efforts in the field of public health in relation to other complex health problems.
However, the issues are far from resolved and feel very new to the field of obesity
because it has heretofore been oriented to treatment rather than public health and pre-
vention. Considering these issues in relation to obesity prevention has the potential to
advance the field of public health generally while also meeting the immediate need for
clarity on evidence issues related to addressing the obesity epidemic.
Study Charge
Recognizing the importance of the issues outlined above, the IOM formed the
Committee on an Evidence Framework for Obesity Prevention Decision Making,
with funding from the Centers for Disease Control and Prevention (CDC), Kaiser
Permanente, and the Robert Wood Johnson Foundation. The IOM appointed the
16-member committee in November 2008 to address the issues of how to identify,
use, and evaluate evidence to inform obesity prevention decisions and how to generate
evidence where it is lacking. These issues were identified as being of major concern or
relevance to a range of potential users: decision makers in government and the private
sector, practitioners in public health and other sectors, and program evaluators and
other public health researchers, as well as research funders, journal editors, and the
media, which determine, respectively, what research is funded, published, and dissemi-
nated. The committee members were selected to include academic researchers, practi-
tioners, and policy makers, representing content expertise in various aspects of child
and adult obesity prevention interventions; public health policy practice and research
more generally; and research methodology from the perspectives of biomedicine, edu-
cation, and psychology.
The committee was tasked to:
• provide an overview of the nature of the evidence base for obesity prevention as
it is currently construed;
• identify the challenges associated with integrating scientific evidence with broad-
er influences on policy and programmatic considerations;
• provide a practical and action-oriented framework of recommendations for how
to select, implement, and evaluate obesity prevention efforts;
• identify ways in which existing or new tools and methods can be used to build
a useful and timely evidence base appropriate to the challenges presented by the
obesity epidemic, and describe ongoing attempts to meet these challenges;
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• develop a plan for communicating and disseminating the proposed framework
and its recommendations; and
• specify a plan for evaluating and refining the proposed framework in current
decision-making processes.
Study Approach
A variety of sources informed the committee’s work. The committee’s deliberations
drew on the findings and conclusions of the above-referenced IOM reports, and on
other resources from within and outside the United States related to evidence-based
public health and public policy as identified through extensive searches of the litera-
ture and a commissioned paper. Two public workshops were convened, in January
and March 2009, to obtain additional input on evidence uses and challenges and on
systems thinking and methodology (see Appendix F for the workshop agendas).
Obesity prevention differs from obesity treatment in the types of questions being
addressed and answers being sought, the contexts in which the questions are asked
and the answers are applied, and the types of research and information that may be
relevant. The realities of using evidence to inform decisions about obesity treatment
and prevention also differ in the availability of relevant research. In addition, because
many influences on obesity are outside the health domain, information relevant to
obesity prevention may not be readily identified through health research approaches.
Given a dearth of information to address an urgent public health problem, the infor-
mation that is available will be valued differently and efforts to fill evidence gaps
given high priority.
Study Scope
This study was designed to go beyond obesity prevention as such, also yielding guid-
ance for more general efforts to address complex, multifactorial public health chal-
lenges and examining the application of a systems perspective to the contexts in which
policy and programmatic decisions that address such challenges are made. Equally
important, the study scope was defined to reflect the need for a framework to guide
decision making about obesity prevention in the population at large, rather than
only in relation to children and youth. The epidemic of obesity in children and youth
continues to be a major driver of preventive initiatives, but obesity prevention is also
relevant to adults. As noted earlier, most obesity and obesity-related diseases develop
during adulthood, and an obese adult population contributes to the development of
obesity in children; indeed, from a population perspective, the environments of chil-
dren and adults are interdependent and inseparable.
The committee defined “framework” to mean a process for identifying, evaluat-
ing, and compiling evidence relevant to various obesity prevention decision-making
scenarios based on clearly specified concepts, assumptions, or rules. The process of
developing the framework involved:
Introduction

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• clarifying what is meant by population-based obesity prevention, that is, the
types of initiatives that are undertaken to improve environments for eating and
physical activity in ways that will reduce the likelihood of excess weight gain
among people in general, as well as among particularly high-risk populations;
• envisioning potential users and uses of such a framework, including the types
of decisions to be made and ways in which evidence might enter into these
decisions;
• assessing the strengths and limitations of current approaches to evaluating and
generating evidence about obesity prevention; and
• identifying research approaches and forms of evidence that could be used to
expand the options available to inform decision making on obesity prevention.
The assessment of the strengths and limitations of current approaches included
a review of several ongoing efforts to improve research and practice in the field of
obesity prevention or public health. These efforts focus on improving methods for
characterizing the strength of evidence for prevention approaches, incorporating issues
of generalizability of the research or relevance to practice into effectiveness studies,
identifying appropriate outcome measures for obesity prevention, or enhancing the
reporting of the results of prevention studies. Appendix B describes these efforts.
This report has two primary audiences: (1) decision makers and the intermediar-
ies who assist them in making decisions and (2) because much of the evidence that is
needed does not now exist, those who conduct research relevant to obesity prevention
or who evaluate existing programs, as well as research-trained academics or other pro-
fessionals with direct access to and knowledge of methods of evidence review and syn-
thesis. Other important audiences include research funders and publishers of research
findings.
OBESITY AS A SOCIETYWIDE PROBLEM
Overweight and obesity—reflecting a gain of excess body fat—result from the cumula-
tive and initially imperceptible effects of hour-to-hour and day-to-day eating and phys-
ical activity behaviors that create a surplus of calories consumed relative to calories
expended. Excess weight gain is usually unintentional and gradual, and it is difficult
to reverse on a permanent basis.
Obesity prevention includes the need both to help those who are already over-
weight or obese avoid further weight gain and to help people who are not overweight
or obese to avoid gaining excess weight. As suggested above, even if all those who are
currently obese were to be treated effectively today, growth in the numbers of people
becoming obese would continue without preventive efforts. Trend data from the
National Health Examination and the National Health and Nutrition Examination
Surveys between 1960 and 2002 indicate that the average body weight of U.S. men
and women increased by 24.7 pounds (11.2 kg) and 24.1 pounds (11.0 kg), respec-
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tively, while there was a relatively small increase in average height. The associated
shift in average body mass index (BMI)—the typical weight-for-height measure used to
assess obesity—was 3 kg/m2 in adults, in both men and women, from approximately
25 to 28 (Ogden et al., 2004). Figure 1-1 shows the shift in the distribution of BMI
among U.S. adults between 1976-1980 and 2005-2006, with the gain being most pro-
nounced among the heaviest people (Ogden et al., 2007).
Data from the 2007-2008 National Health and Nutrition Examination Surveys
(NHANES)2 show that among adults aged 20 or older, nearly 34 percent have weight
levels in the obese range (BMI ≥ 30) and another 34 percent are classified as over-
weight (BMI between 25 and 30), thus the combined prevalence of overweight and
obesity is nearly 68 percent (Flegal et al., 2010). Among children and adolescents
aged 2 through 19, nearly 17 percent are classified as obese (BMI for age and sex
≥ 95th percentile), and 15 percent are classified as overweight (BMI for age and sex
≥ 85th but < 95th percentile), thus close to 32 percent are either overweight or obese
(Ogden et al., 2010). There is no evidence that underlying biological susceptibility to
weight gain has changed, although there is ample evidence of increases in such factors
as the amount of food available and where it is available, creating eating environ-
ments that are highly conducive to the consumption, often unintentional, of excess
calories (Kral and Rolls, 2004; Ledikwe et al., 2005; Story et al., 2008; Wansink,
2004). There is also no evidence that the prevalence of individual weight control
attempts has decreased as average population weights have increased. For example,
the proportion of U.S. adult men and women who reported attempting to lose weight
was, respectively, 29 and 44 percent in 1996 and 33 and 46 percent in 2000 (Bish
et al., 2005; Serdula et al., 1999). Accordingly, the increasing prevalence of obesity
in diverse populations reveals the limitations of biological and behavioral controls on
caloric balance in the face of high caloric availability and the relatively low levels of
physical activity that are common in urban and westernized societies (Booth et al.,
2001; French et al., 2001; IOM, 2005; Kumanyika et al., 2002; Popkin and Gordon-
Larsen, 2004). The need for multifaceted actions to prevent obesity should no longer
be a subject of serious debate.
Many multifaceted interventions for obesity prevention influence the calorie
balance by focusing on either energy intake or energy expenditure. According to
Swinburn and colleagues (2009), it is important to know whether one of these two
factors is the primary driver of the obesity epidemic in order to prioritize potential
interventions. The relative contributions of increased energy intake and decreased
energy expenditure to the obesity epidemic have been debated, with some suggesting
that increased energy intake is sufficient to explain the weight gain of the American
population since the 1970s (Bleich et al., 2008; Swinburn et al., 2009). Both factors
are clearly important for energy balance and other health outcomes, and this report
does not aim to tell decision makers whether to focus on energy intake, energy expen-
2 NHANES is a continuous program of studies designed to assess the health and nutritional status of a nationally representative sample of
children and adults in the United States.
Introduction

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20
15
Percent
NHANES 1976 -1980
10
5
NHANES 2005 -2006
0
10 15 20 25 30 35 40 45 50
B MI
FIGURE 1-1 Changes in the distribution of body mass index (BMI) between 1976-1980 and 2005-2006 among U.S. adults
aged 20-74.
NOTE: NHANES = National Health and Nutrition Examination Survey, a continuous program of studies designed to assess the
Figure 1-1.eps
health and nutritional status of a nationally representative sample of children and adults in the United States.
SOURCE: Ogden et al., 2007.
diture, or both. Indeed, the relative importance of each may vary across populations
and settings.
Figures 1-2 and 1-3 show recent levels of obesity in three racial/ethnic groups
in the United States and projections of future prevalence under the assumption that
recently observed rates of increase will continue (Wang et al., 2008). The approxi-
mately one-third of men in all three groups who were obese in 1999-2004 could
increase to nearly one-half within two decades. The same could be true for non-
Hispanic white women, with even higher levels for non-Hispanic black and Mexican
American women, for whom the prevalence of obesity was already greater than
50 percent and 40 percent, respectively.
Prevention efforts should not only aim to improve weight levels in the popula-
tion at large but also target subpopulations with higher-than-average risk. Figures 1-2
and 1-3 identify key high-risk population subgroups—Mexican Americans and
African Americans (Hedley et al., 2004; Ogden et al., 2007). Other U.S. ethnic groups
with above-average obesity prevalence include American Indians, Pacific Islanders,
and Native Hawaiians (Anderson and Whitaker, 2009; Broussard et al., 1991; Davis
et al., 2004; Kumanyika, 1993). Low-income children and youth are also at high risk
for obesity.
In many cases, above-average obesity prevalence is also observed in low-income
populations, or high income is associated with lower obesity prevalence. In adults, the
inverse gradient in obesity levels is seen most clearly in white females (Ogden, 2009).
Figure 1-4 shows data for children with both sexes combined (Freedman et al., 2007).
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Non-Hispanic white Non- Hispanic black Mexican American
30 27
25 22
21 21 21
Percent Obese
19
20 18 18
17 17
15 15 14
15 12
11
10
5
0
<1
9
9
9
4+
<1
9
9
9
4+
<1
9
9
9
4+
1.
2.
3.
1.
2.
3.
1.
2.
3.
1-
1-
1-
2-
2-
2-
3-
3-
3-
Poverty– Income Ratio
FIGURE 1-4 Percent of children and youth aged 2-19.9 who are obese (defined as BMI ≥ 95th percentile based on CDC
growth charts), by family poverty−income ratio.
Figure 1-4.eps
NOTES: The poverty−income ratio is the ratio of the income of the family to family income at the poverty level. Families with
an income ratio of < 1 are below the poverty threshold.
SOURCE: Freedman et al., 2007.
While obesity is a priority from an epidemiologic and health status perspective,
it gains further precedence because of the way it influences other aspects of American
society. Obesity carries substantial direct and indirect costs for the nation’s economy,
such as discrimination, economic disenfranchisement, lost productivity, and disabil-
ity. As a result, states and communities end up diverting resources to prevention and
treatment, and the nation’s health care system is burdened with the comorbidities of
obesity, such as type 2 diabetes, hypertension, cardiovascular disease, osteoarthritis,
and cancer (IOM, 2005). According to a recent analysis (Finkelstein et al., 2009), the
annual medical burden of obesity is nearly 10 percent of all medical spending and
may have risen to $147 billion per year by 2008. Further, obesity places at risk the
long-term welfare and readiness of the U.S. military services by reducing the pool of
individuals eligible for recruitment and decreasing the retention of new recruits (IOM,
2005). In addition to these societal costs, obesity imposes a broad range of costs on
individuals. Tables 1-1 and 1-2, respectively, highlight the myriad effects of adult and
child obesity on physical and mental health and quality of life.
DECISION MAKING, OBESITY PREVENTION, AND EVIDENCE NEEDS
In an ideal world, perhaps, policy decisions would be made primarily as a result of
review and analysis of a carefully selected body of evidence that provided certainty
and specificity as to the best approach or approaches, the outcomes that would result,
and the cost of achieving those outcomes. However, real-life experience demonstrates
that policy or programmatic decision making is not always such a linear process and
that initiatives grounded in an idea generated by a research study may be the excep-
tion. Formal evidence may be used in highly variable ways, at different stages of a
Bridging the Evidence Gap in Obesity Prevention
26

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from happening) may be a much less dramatic or salient outcome than treatment
(removing a problem), whose effects are not only obvious but also potentially more
rewarding—personally and politically. Thus, although the case for prevention is com-
pelling, making the decision to give it priority and determining which strategies will
lead to more “nonevents” are highly challenging.
The widely held conviction that such decisions should be “evidence-based” only
increases the challenge. How does one best determine which aspects of the environ-
ment to change, what changes to make, and how to effect these changes? Which inter-
ventions can potentially be effective on a large scale and sustainable over time? Where
are the synergies among interventions? Could there be undesirable effects not readily
apparent at the outset? Ideally, there would be a firm and comprehensive evidence
base to inform the myriad decision makers whose actions—intentionally or uninten-
tionally—influence the social and environmental determinants of unwanted weight
gain and obesity. In reality, the approaches to evidence that apply to decision making
about the treatment of obesity or other clinical problems are inadequate and some-
times inappropriate for application to decisions about public health initiatives such as
obesity prevention. This situation poses a dilemma, one that is clearly compounded by
the urgency of deciding which interventions can best address the problem. Evidence is
needed to support such decisions for many reasons:
• to justify interventions generally, particularly when there is competition for
resources or opposition;
• to inform priority setting and justify actions targeting high-risk populations,
differentiate actions that are likely to be effective from those that are not, and
quantify likely impacts;
• to estimate costs and cost-effectiveness and anticipate unintended consequences,
including harms to individuals or businesses; and
• to help understand implementation factors, that is, what to do and how to do it.
The purpose of this report is to present a framework that will make it possible to meet
these evidence needs.
Figure 1-5, which illustrates the levels and sectors of influence on obesity in
populations, is helpful for understanding why decisions about obesity prevention are
so complex (IOM, 2007). The figure shows the variety of levels at which interven-
tions may be aimed and demonstrates how, taken together, a set of actions across
levels might interrelate. Actions within many of these levels are focal points for dis-
cussion on how to combat the obesity epidemic within the United States and glob-
ally. Pathways or logic models can be drawn to link these levels to weight-related
behaviors of population groups and individuals, such as food purchases; intakes of
sugar-sweetened beverages, fruits and vegetables, whole grains, and total calories; tele-
vision watching and other screen time; automobile use; breastfeeding; and routine and
recreational physical activity. Relevant initiatives might focus on international trade
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• Government
• Public Health
Social Norms • Health Care
• Communities and Values
• Agriculture
• Worksites
• Education
• Health Care
Sectors of • Media
• Schools and
Influence • Land Use and
Child Care
Transpor tation
• Home
• Communities
Behavioral • Foundations
Settings
• Industry
- Food
• Demographic Factors
Individual
(e.g., age, sex, SES, - Beverage
race/ethnicity)
Factors - Restaurant
• Psychosocial Factors - Food Retail
- Physical Activity
Food and Physical
• Gene-Environment
- Leisure and
Beverage Intake Activity
Interactions
Recreation
• Other Factors - Entertainment
Energy Intake Energy Expenditure
Energy Balance
FIGURE 1-5 Comprehensive approach for preventing and addressing childhood obesity.
Figure 1-5.eps
NOTE: SES = socioeconomic status.
SOURCE: IOM, 2007.
agreements that affect the food supply, food advertising, retail and restaurant food
locations and marketing practices (including labeling and portion sizes), food prices,
agricultural policies and food production systems, community design aspects that
influence outdoor activity, building design aspects that influence indoor activity, public
transportation, insurance coverage for wellness services, poverty levels, funding lev-
els for and regulations guiding federal nutrition assistance programs, and school and
worksite environments related to food and physical activity (IOM, 2009; James et al.,
2006; WHO, 2004; World Cancer Research Fund and American Institute for Cancer
Research, 2009).
Obesity prevention initiatives related to the settings and pathways shown on
Figure 1-5 are ongoing, and more are undertaken or proposed every day. Many are
quite far-reaching in their potential implications for such variables as food prices;
food availability; community infrastructure; entertainment; and the nature and flow
of information about food, activity, and weight. When the needed evidence exists
to inform these decisions, the challenge is how to ensure that it appears in the right
place at the right moment in the decision-making process and is taken to heart. If the
evidence that exists is faulty or biased, the challenge is how to prevent this evidence
from being used to support decisions that will ultimately prove to be poor ones. If the
evidence is inadequate, one challenge is to prevent the lack of evidence from preclud-
Introduction

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ing timely and needed best guesses about potentially helpful solutions; another is to
create the evidence to fill the gap. In the dynamic context of such issues as the obesity
epidemic, the uneasy but necessary balance among making use of the best available
evidence, avoiding the pitfalls of poor evidence, taking reasonable actions in the face
of absent or grossly insufficient evidence, and waiting for the long process of formu-
lating and generating relevant new evidence is a key challenge facing decision makers.
Guidance is needed to keep a fruitful balance in view as progress toward solutions
is made.
Box 1-1 presents some decision scenarios related to obesity prevention poli-
cies and programs. Those shown in italics are decisions likely to be made based on
priorities unrelated to obesity but with potential effects on eating or physical activity.
The decision scenarios in Box 1-1 all relate in some way to decisions about interven-
tions; these types of questions are central to obesity prevention. However, decisions
about the selection, implementation, and evaluation of interventions are closely tied
to questions about why the intervention is needed and how a specific intervention
can be expected to work in a given context. Some of these scenarios illustrate the
potential for making arguments on obesity issues to justify changes in well-established
policies and practices that affect marketing, services, or infrastructure related to pat-
terns of eating and physical activity so as to ultimately influence consumer behavior.
Consideration of these types of scenarios was core to the committee’s deliberations,
undertaken to ensure that the resulting framework would be practical and broadly
relevant.
ORGANIZATION OF THE REPORT
The remainder of this report is organized as follows:
• Section I provides background on obesity prevention concepts and approaches
(Chapter 2) and on evidence issues, including the results of the committee’s
review of the limitations of current approaches to evaluating obesity prevention
research (Chapter 3). Chapter 3 also introduces the committee’s proposed frame-
work for using evidence to inform decision making on obesity prevention.
• Section II presents an elaboration of each component of the proposed frame-
work (Chapters 4 through 8). The importance of taking a systems perspective
and how such a perspective can be useful in the process of using evidence to
inform obesity prevention decisions is discussed in Chapter 4. Chapter 5 pres-
ents a typology of decisions and evidence that can guide the task of identifying
useful evidence, a classification and discussion of various forms of evidence,
and guidance on the process of searching for evidence. Chapter 6 explains the
committee’s recommended approach to evidence evaluation as embodied in the
framework; the discussion includes references to resources that can be useful in
assessing the credibility of different forms of evidence. Chapter 7 addresses the
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Box 1-1
Decision Scenarios Related to Obesity Prevention Policies and Programs
Decisions about spe- • A local board of health or city council considers a proposal to require that menus of
cific, populationwide chain restaurants show the calorie content of each item.
policy changes with a • A state legislator decides whether to vote for or against a measure to tax sugar-
potential direct impact sweetened beverages as an obesity prevention measure.
on physical activity or • A city planning authority is considering closing city center streets to automobile use to
weight-related behavior reduce traffic flow and increase pedestrian access to local businesses.
of adults or children • A federal authority is attempting to determine whether there are sufficient grounds to
implement statutory restrictions on television and Internet advertisements directed at
children.
• A school board member decides whether to vote for a measure to send parents reports
of their children’s BMI levels based on annual weight and height screening.
Decisions to undertake • A school board is considering a policy that would remove sugar-sweetened beverages
or retain a specific pro- and snack foods from schools in its district.
gram that would affect • The director of a youth service organization is about to select a family-oriented nutrition
access to food or physi- and fitness program for nationwide implementation.
cal activity options • A state education authority is faced with a decision to cancel the requirement for
daily physical education classes to make room for additional academic content in the
curriculum.
• A local foundation is considering a proposal to fund a program to create a network of
farmers’ markets in low-income neighborhoods.
• An economically strapped city is considering cuts in funding for local parks and recre-
ation centers.
• A community development corporation has been asked to partner in an initiative to
establish a supermarket in a low-income neighborhood.
• The state comptroller may have to cut funding for school bus service in certain
neighborhoods.
• A prior mayor instituted a program to link after-school programs that focus on academ-
ics and sports. The current mayor is trying to decide whether to continue the program.
Decisions about which • A state health commissioner who has been given 5 years to show progress in reducing
intervention(s) to select childhood obesity rates among low-income communities needs to develop a strategic
from a set of potential plan.
options to decrease • An employer is negotiating what package of wellness services will be included in the
obesity-promoting envi- employee benefit package.
ronmental influences • A community-based organization is seeking ways to increase access to more healthful
foods for residents of a rural community.
• A state-based obesity prevention coalition is trying to identify advocacy priorities to
address childhood obesity.
• A budget director is attempting to weigh the potential cost-effectiveness of a taxation
strategy and complementary social marketing campaign to reduce population obesity
levels.
NOTE: Scenarios shown in italics are decisions likely to be made based on priorities unrelated to obesity but with potential effects on
eating or physical activity.
Introduction

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processes of assembling and reporting results, translating evidence to and from
practice, deciding on the implications of the information for decision making,
and integrating the overall knowledge gained from the evidence review process.
Chapter 8 addresses the need for researchers to use the framework to motivate
their work and think systematically about how to make progress in the inevi-
table, ongoing context of inadequate and imperfect evidence, and highlights
other approaches to evidence generation for increased use in research on obesity
prevention.
• Finally, Section III turns to next steps. Chapter 9 provides guidance for future
efforts of communicating, disseminating, refining, and updating the framework
as new evidence and new methods emerge. Chapter 10 summarizes the commit-
tee’s conclusions and presents recommendations for supporting the identifica-
tion, use, and evaluation of evidence to inform obesity prevention decisions and
generate evidence when it is lacking.
For reference throughout the report, a list of acronyms and glossary of terms
is provided in Appendix A; a table listing current efforts to improve research and
practice in the field of obesity prevention or public health is given in Appendix B;
Appendix C contains a table listing current reviews of obesity prevention interven-
tions and strategies; Appendix D provides a list of selected information sources for
locating evidence; Appendix E presents an in-depth discussion of some study design
alternatives to randomized controlled trials and how theory, professional experience,
and local wisdom can be used when evidence is lacking; Appendix F contains the
agenda of two public workshops held by the committee; and Appendix G presents
biographical sketches of the committee members.
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Bridging the Evidence Gap in Obesity Prevention